Miele PDR 908 EL Operating And Installation Instructions page 72

Installing the ducting
Shared exhaust-air duct
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Damage and impairment to the tumble dryer and its electrical safety as a
result of condensation.
Condensation in the shared exhaust-air duct can run back into the tumble dryer
and cause damage.
Install the shared exhaust-air duct onto the tumble dryer in accordance with
these operating instructions.
A = Drain for condensation
A drain must be installed on the shared exhaust-air duct.
R = Non-return flap
The non-return flap is installed directly on the shared exhaust-air duct.
D = Pipe diameter
Depends on the number of tumble dryers installed
A maximum of 5 tumble dryers may be installed on a shared exhaust-air duct.
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